The invention relates to an arrangement in a frequency converter.
A frequency converter is a device by which rotation rate of an AC motor, such as a squirrel-cage motor, is adjusted steplessly. The rotation rate adjustment is carried out in the frequency converter mainly by changing the voltage supplied to the motor and the voltage frequency. The frequency converter allows to adjust acceleration and deceleration, as well as slowing down and reversing of the motor. When the frequency converter is used for controlling the motor, it is possible to perform the adjustment and control of the motor by a computer in a control unit.
A problem with the current frequency converters is that a frequency converter applicable to the control of a motor of a specific size is a compact device, in which all the structural parts of the frequency converter are arranged mutually integrated in one and the same casing. The frequency converter mainly comprises a power part, which consists of means for converting alternating current to direct current and back to alternating current with adjustable frequency, and a control and adjustment part, which consists of means for controlling and adjusting the operation of the power part and thus the operation of an electric motor. In the prior art solution, only the display and the control panel of the frequency converter are placed in the casing cover of the frequency converter and connected with a cable to a control and adjustment part inside the casing.
The frequency converter that is designed and assembled to be compact in this manner has disadvantages, because it is problematic to provide both electromagnetic protection and shielding from contact for the power part and the control and adjustment part that are located mutually integrated in the same casing. It is known that power electronics of the power part produce large amounts of interfering electromagnetic radiance, which is harmful to the operation of the electronics in the control and adjustment part. Secondly, in an integrated solution of this kind it is particularly important to pay attention to the shielding of high voltage components of the power part from contact, so that the safety requirements of the frequency converter can be fulfilled. In addition, the frequency converter technology develops towards modular structure solutions, in which the power part and the control and adjustment part are divided into separate components. Complicated shielding solutions having a large number of separate parts are, in general, uneconomical.
The object of the present invention is to reduce disadvantages of the prior art and to provide a novel solution to arrange a control part of a frequency converter in a casing of the frequency converter.
This is achieved with a frequency converter having the characteristics defined in the claims of the present invention. To put it precisely, the frequency converter according to the present invention is mainly characterized by what is disclosed in the characterizing part of claim 1.
The preferred embodiments of the invention are disclosed in the dependent claims.
The invention is based on the idea that a power part and a control and adjustment part of a frequency converter are separated from one another to be separate modules and arranged in a set of casings consisting of one or more casings. At least one casing of the set of casings comprises an openable cover part, in which the control and adjustment part of the frequency converter is arranged. This cover part comprises an opening, in which is arranged an embedding frame comprising a frame part that connects the frame part to the cover part and a substantially enclosed tub-like recess that substantially protrudes inside the casing from the frame part, whereby the control part of the frequency converter is arranged in the tub-like recess of the embedding frame.
Because the structural parts of the frequency converter are divided into two separate units and separated from one another with the embedding frame, a considerable advantage is achieved that the embedding frame constitutes a structure that protects the control and adjustment unit in a variety of ways and simplifies the structure of the frequency converter regarding installation and maintenance, which improves the cost-effectiveness of the frequency converter. This enables maintenance and handling of the control and adjustment part without opening the whole casing cover of the frequency converter, i.e. the control and adjustment part mounted in the embedding frame is readily accessible, as if it were placed outside the casing, but still, it is physically within the external dimensions of the casing.
On the other hand, if the circuits of the power part of the frequency converter need to be accessed for maintenance or handling, the control and adjustment part, when mounted in the openable cover part of the casing and the embedding frame arranged therein, allows free access to the main circuits when the cover part is opened, whereby accessability and serviceability of the power part of the frequency converter implemented by this solution are improved, and consequently, the cost-effectiveness is improved.
A cover part that closes tightly the recess of the embedding frame is arranged on the embedding frame. This has an advantage that the embedding frame and the cover part form a structure around the control and adjustment part, which is located in the recess of the embedding frame, that provides protection against humidity, dust, gas and the like environmental factors, which structure can be sealed to comply with the necessary IP protection class standard.
The embedding frame is made of an electromagnetically protective material, such as metal, whereby the embedding frame forms a structure around the control and adjustment part, which is located in the recess, that advantageously provides protection against electromagnetic radiation and reduces electromagnetic disturbances that the power part causes to the control and adjustment part.
The recess of the embedding frame is designed and formed such that the control and adjustment part mounted in the embedding frame is substantially in the tub-like recess of the embedding frame, whereby the embedding frame provides a mechanically protective structure for the control and adjustment part in the recess. Thus the control and adjustment part is provided with effective, mechanical protection inside the casing, and on the other hand, it is electrically isolated from the power part.
Further, the embedding frame is arranged to provide shielding against contact between the control and adjustment part in the recess and the power part in the set of casings. This improves work safety in mounting situations, because the high-voltage components of the frequency converter can be effectively shielded against contact by encapsulation of the power part and the control and adjustment part implemented by the embedding frame.